Thursday, May 31, 2012

As discussed in 'Importance of Nitrogen in Winemaking',
proteins represent a significant portion of wine's total nitrogen content. Proteins synthesized during berry development account for approximately
half of total wine protein, a small portion is derived from yeast protein synthesis during fermentation, and the remainder from
yeast autolysis. Protein levels in grapes and resultant wine
depend on several variables, including viticultural and winemaking
factors.

The solubility of wine proteins is highly dependent on temperature, alcohol concentration, and pH. Typical wine pH levels are very near most wine proteins' isoelectric point (where positive and negative charges are equal). Proteins have a negative charge when pH is above the isoelectric point, and vice versa. This plays a major role in protein stability and determining what fining agents to use on particular wines.

Phenolics play a major role in protein stability due to their interactions with proteins. Wines with high polyphenol concentrations will often remove a sufficient amount of proteins to make the wine stable; thus, white wines and lower phenol red varietals have more issues with protein instability (color loss and instability in red varietals such as Pinot Noir are highly correlated to protein concentration). Due to the tannins in wood, wines fermented or stored in barrels also have far less problems with protein stability when compared to those held in stainless steel.

Winemakers all have varying opinions on the best (or most efficient) way to monitor fermentation. These opinions will be largely dependent on several variables such as facility size, harvest pace, staffing, and ferment type (tank, barrel, fast, slow, etc.). I tend to be rather meticulous (colleagues will tell you my obsession with spreadsheets and charts is very beneficial in this regard); my main goal is to track as much as I can about individual lots so that I can ensure successful fermentation while gathering data that will be useful in future vintages.

My first priority is having accurate analysis prior to inoculation. The completeness of this analysis really depends on the laboratory, but ideally I like to have brix, pH, TA, YAN, free and total SO2, malic acid, temperature, and VA. These analyses should take into account any amendments made to the juice/must since arrival at the winery, providing a good baseline to track that ferment is proceeding healthily and a good starting point for any additional ferment amendments desired.

I like to create Fermentation charts (dates vs.
brix and temperature) to be able to visualize how fermentation is
proceeding. These help with decisions involving amendments,
temperature adjustments, cap management (for red must), and stopping fermentation (if residual sugar is
desired), not to mention planning fermentation tank turnover time
for future vintages. Any nutrients should be added before brix levels are too low (I usually aim for 1/3 or 1/2 sugar depletion for secondary additions of fermentation nutrients and nitrogen supplements). If undesirable odors/flavors appear later in fermentation, then additional amendments of nutrients should be done prior to brix falling below 2/3 depletion.

Depending on how the juice/must is inoculated, it can be a matter of hours or days until the yeast really starts fermentation (indigenous yeast ferments will have the longest lag phase, while propagated inoculations will often start immediately). Typically, I work on a 24-hour ferment check, not only analytical (brix and temp) but also sensory; if this shows anything strange, then further analysis may be desired.

Barrel ferments are often more difficult to track accurately compared to those in tank. This is due to variability between barrels (I've worked with barrel groups from one to several hundred in number) and less temperature control. 24-hour ferment checks on barrel groups are often too time-consuming for laboratory staff, so these will usually be monitored less frequently (every few days) granted they are fermenting healthily.

If stopping fermentation with residual sugar is desired, I'll create a brix target to mark the beginning of residual sugar (RS) checks. This will hopefully be a couple days in advance of the ferment reaching the target RS to ensure it is under control and stopped on target. For ferments aimed at dryness (less than 2 g/L RS), RS checks can begin once the ferment reaches -2° brix (or maintains a negative brix reading for several days).

Sunday, May 20, 2012

No matter what you want to call it, sate (or satay) is another dish that originated on Indonesia's island of Java, but has become popular throughout Southeast Asia. Sate consists of skewers of meat chunks (usually chicken, pork, or lamb) marinated and grilled.

Finding sate in Indonesia is not difficult. Here in Bali, it can be found in plenty of high-end restaurants and street-side warungs. but really you just need to keep an eye out for the small rectangular barbeques smoldering away on the side of the street. Of course, everyone has a different take on Sate and what sauce to accompany it with; this is highly dependent on regional preferences, but my favorite (and one of the most common) consists of peanuts, garlic, shallots, tumeric, and kecap manis (sweet soy sauce).

Thursday, May 17, 2012

I received a few comments regarding my recent post on YAN via LinkedIn. I summarized the comments made by other users and added my responses below.

Comment Summary

If this is so, how come good wine is made without this technique? It
may ensure that you don't have problems, but I add all nutrients in near inoculation time.

Maybe the
practice is better for fruit forward and the high alcohol wines.

DAP is considered yeast junk food, it's pretty much like us eating pure sugar. Fermentation nutrients such as Yeastex and Superfood are better.

Unused DAP can result in the
formation of the carcinogenic compound ethyl carbamate so it must all be
added with caution and only during the first half of fermentation to
ensure it is all used up.

An early stinky ferment is best caught very early and aerated to provide sufficient oxygen for yeast to build sterols into their cell walls. Sterols are important for nitrogen transport and ensure plant-derived YAN is efficiently used.

My Responses

I've always loved the mantra that 'great wine is made in the vineyard'.
As a winemaker, I don't believe in adding anything unnecessary; great
wine can be made without the addition of anything (nutrients, enzymes,
tannins, etc.) but requires excellent fruit quality.

As indicated, adding all nutrients at the beginning of ferment is often
not a problem and a very common practice. Adding in stages is a safer
practice, particularly in the case of highly nitrogen deficient must
(for instance, higher brix must).

DAP can be equated to pure sugar consumption by humans; it is the easiest compound for yeast to derive
necessary nitrogen. I always suggest using fermentation nutrients in
conjunction with DAP (or in lieu, of depending on how nitrogen deficient
must is). Bear in mind that these blends only supply a fraction of the
YAN that DAP would; for example, 100 ppm of Superfood provides
approximately 7.75 ppm YAN while the same weight of DAP provides 22.5.

The
main precursor of ethyl carbamate (otherwise known as urethane) is
actually urea, who's main precursor is arginine (very common amino acid
found naturally in grapes). Urea is formed during early and middle
stages of normal alcoholic fermentation, then utilized by yeast in later
generations. 'Stop ferments' (fortified wines or wines stopped sweet)
have a much higher propensity to lead to ethyl carbamate issues since
they are often stopped when urea levels are still high. Urea production
during fermentation is highly dependent on yeast strain.

The reason DAP has been indicated to lead to ethyl carbamate production
is because adding too much DAP (particularly at the beginning of
fermentation) will stop yeast from metabolizing free amino acids
(including arginine). So, caution is definitely required.

Oxygen additions during fermentation can be very beneficial. As you
indicated, oxygen is necessary for yeast to synthesize lipids and
sterols to produce properly functioning cell membranes. Yeast are what
is referred to as facultative organisms, they can operate aerobically
and anaerobically. Oxygen is consumed very rapidly at the onset of
fermentation (usually within the first few hours), so yeast switch from
aerobic to anaerobic fermentation; once this occurs, yeast cannot
synthesize these building blocks and must rely on those already in
solution. Your addition of oxygen curing your stinky ferment is more
likely helping alleviate a stressed yeast population that wasn't
adequately prepared to switch from aerobic to anaerobic activity.

Monday, May 14, 2012

Once the YAN level is determined for a particular juice/must, the winemaker can decide how much and when additional nitrogen will be required (this is not an exact science, but the chart here gives a pretty good estimation of the total amount of YAN required through fermentation; basic rule is the higher the brix, the higher required YAN).

The most common nitrogen supplement used in the wine industry is
diammonium phosphate (DAP). DAP provides approximately one-fourth of its weight in assimilable nitrogen (to be extact, 100 ppm of DAP will provide 22.5 ppm of assimilable nitrogen). It is often used in conjunction with
proprietary fermentation nutrient blends (most of which provide small amounts of nitrogen, but more importantly essential micro-nutrients). Winemakers need to be cautious about overusing DAP; yeast will preferentially take up ammonia ions over amino acids, whose synthesis provides a significant source of aroma and flavor precursors.

Timing is a major concern when planning nitrogen supplementation of juice/must. Depending on how much nitrogen is required, I
like to add approximately half at the beginning of fermentation and the
remainder after approximately one-third brix decrease; this provides the yeast with a steadier
nitrogen supply to carry through the end of fermentation and, if necessary, leaves room for a small addition if undesirable odor/flavor appears later in ferment.

It is not wise to add it all prior to inoculation; high YAN levels at the beginning of fermentation promotes rapid cell growth that can lead to overpopulation of yeast. This in turn depletes YAN at an abnormally high rate and leads to a lot of unhappy yeast producing undesirable odors and flavors through the duration of fermentation. On the other hand, nitrogen supplementation late in ferment is often useless; yeast can uptake nitrogen throughout their growth phase, but alcohol inhibits uptake about halfway or two-thirds through fermentation (i.e. with 8-10° brix left when starting with 22° brix). This means late supplementation of nitrogen will basically have little or no effect on fermentation kinetics or undesirable odor/flavor production; that being said, I know plenty of winemakers (I admit I have done this on rare occasions as well) that will add nitrogen down to 5° brix in the hopes of reviving a troublesome ferment.

Thursday, May 10, 2012

As discussed in 'Importance of Nitrogen in Winemaking',
there are several types of nitrogenous compounds to be
concerned about during the winemaking process. Yeast assimilable
nitrogen (YAN) is the combination of ammonia and freeamino acids
that are metabolically available to yeast during fermentation. Winemakers use the YAN
value to determine if and how much nitrogen supplementation is required
for a successful fermentation.

Nitrogen
is considered the most limiting factor during fermentation. Lack of
nitrogen in juice/must creates several different problems for yeast
during fermentation: low yeast biomass (slow fermentation rate),
inability to synthesize glucose transport proteins, and decreased
ability to act under adverse conditions (high ethanol levels, high CO2 levels,
extreme temperatures, etc.). Not only does this mean a high risk of
incomplete fermentation, it also means high stress levels that will
likely lead to the production of undesirable odors and flavors.

Besides
avoiding the negative effects associated with nitrogen deficiency,
there is a strong correlation seen between nitrogen levels and wine
aroma/flavor intensity; wines fermented with sufficient YAN tend to have
lower production of long-chain alcohols, aldehydes, and undesirable
odors/flavors, while having higher production of low molecular weight
esters and beneficial autolysis products.

The minimum amount of YAN required for a successful fermentation of normal table wine (i.e. juice/must with a starting brix of
21°) is 140 mg/L. Many wine scientists and
winemakers (including myself) contend that this is far too low and highly likely to lead to an unsuccessful fermentation. I created the chart below as a guideline for brix
and typical desired YAN value.

Since yeast uptake assimilable nitrogen rather quickly after the onset of fermentation, YAN needs to be measure prior to inoculation. YAN is the combination of the concentration of ammonia ions and the concentration of free amino acids (determined via two separate lab analyses). If the YAN level is found deficient for successful fermentation, the juice/must needs to be supplemented with additional nitrogen.

Wednesday, May 9, 2012

I find it funny when people ask me, "you're surfing a single-fin out here?" Some people really need to learn their history, especially when it comes to surfboard design; Bali surfing began in the 1960's and 70's, with surfers riding single-fins. Timeless Padang Padang barrel on my Alexander Surfboards 6'9" single-fin, photo by Trevor Murphy.

Monday, May 7, 2012

Nitrogen-containing compounds are naturally occurring in grapes and extremely important during their cultivation. In turn, they are also very important during winemaking procedures (particularly during fermentation, clarification, and microbial stability). The total nitrogen content of grapes is highly variable, ranging between 60 and 2,400 mg (N)/L and due to viticultural factors (grape varietal and rootstock, fertilization, grape maturity at harvest, soil, climate, and disease). Nitrogen-containing compounds in juice/must include amino acids, amines, ammonia, peptides, polypeptides, and proteins.

Proteins - Protein synthesis in grapes occurs rapidly after veraison (onset of ripening), at a similar rate as sugar level increase. In juice/must, proteins usually represent less than 10% of total nitrogen content; in wine, levels are far higher and reach up to 40%. This is a bit deceptive because only half of the total wine protein is sourced from grapes. The rest are derived from fermentation; small amounts of protein are released by yeast during fermentation, and large amounts are released during autolysis (yeast breakdown) post-fermentation. Proteins derived from yeast autolysis (extended lees contact will be discussed in a later post) contribute to a wine's mouthfeel. Soluble proteins are of major concern during clarification procedures because their precipitation in bottled wines leads to 'protein haze' or deposits (see Wine Proteins & Stability - Part I and Part II).

Polypeptides - Essentially protein fragments, polypeptides are long polymers of amino acids linked by peptide bonds (chains of peptides). These can represent a very large portion of wine nitrogen content depending largely on processing techniques that breakdown proteins. Polypeptides are important to wine because of their contribution to mouthfeel; the process of sur lie aging (to be discussed in a later post) has a major effect on polypeptide level and enhancing mouthfeel.

Biogenic Amines - Amines are a group of nitrogenous compounds that includes biogenic amines and amino acids. Biogenic amines present in wine result largely from bacterial activity, both from malolactic fermentation or non-desirable organisms (decarboxylation of amino acids by Oenococcus, Lactobacillus, Pediococcus, etc.). They can also be sourced from the grapes themselves, and as by-products of primary fermentation and wine maturation. Usually only present in very small concentrations (less than 0.3 mg/L), biogenic amines can be used as an indicator of spoilage (strong correlation between high levels of biogenic amines and volatile acidity, as well other negative compounds such as butyric acid, acetic acid, ethylacetate, etc.). Biogenic amines levels are typically higher in red wines than whites, and are largely indicated as the cause of wine headaches.

Amino Acids - Amino acids serve as the building blocks for peptides and proteins. The levels of the twenty different amino acids naturally occurring in grapes vary widely depending on grape varietal, viticultural practices, and processing techniques, though total amino acid level at harvest usually falls between 30-400 mg/L. Amino acids are of utmost importance during fermentation due to their metabolic availability to yeast (read about Yeast Assimilable Nitrogen) and their sensory effects in wine (also to be discussed in a later post).

Ammonia - During grape maturation, ammonia levels decrease as protein and peptide levels increase. Typical ammonia levels at harvest range from 20-220 mg/L. Ammonia is also of utmost importance during fermentation due to its metabolic availability to yeast (read about Yeast Assimilable Nitrogen).

Wednesday, May 2, 2012

This is my everyday board that I've had for just over a month now from Alexander Surfboards. It's a 6'1" x 19" x 2 3/8" thruster with a thumb tail and fully inverted vee bottom that transitions into a very slight vee just below the front fins. I've put it through its paces in a lot of different conditions already; I like the speed that it produces, and it transfers rail to rail really well. Jeff set my front fin boxes out at 10 degrees, which helps keep the fins in the water on a hard turn (works really well with my IndoFins F4's). Also check out - 6'9'' Alexander '70's Special' Single-Fin

Tuesday, May 1, 2012

Counterfeit wine has become commonplace in the modern wine industry. With fine-wine trade being primarily unregulated (between purchaser and resellers with no connection to the original vintner), some people have gotten into the business of 'replicating' expensive wines and selling them as real.

This is old news, but I recently came across this article, "The Jefferson Bottles", and thought it was a very interesting read. Not only is it an interesting story, it also provides a lot of information on how wine counterfeiters operate along with how wine experts and scientists authenticate wine.